Plasma surface modification and plasma deposition are widely used commercially to tailor surface properties of many different types of materials.  Numerous examples are to be found in the semiconductor industry, automotive industry and web coating sector.  Plasma coating or plasma polymerisation involves the polymerisation of organic monomer molecules initiated by low temperature plasma conditions.  Advantages of this route of surface engineering include the relatively small quantities of coating pre-cursor used, the low energy requirements of the plasma systems and the substrate independent nature of the process.

XPS plays a central role in the development of the coating procedure.  The success of the deposition process can be monitored in terms of film coverage.  Furthermore, the chemistry of the new formed surface can be investigated and correlated with observed properties.

In this example a low temperature, non-equilibrium radio frequency plasma discharge was used to deposit an ultra-thin low energy surface on fabric.  Using this method desirable, high value, non-wetting characteristics can be conferred onto bulk, low cost materials such as woven cotton or nylon. 

A fluorinated plasma polymer was applied to several different fabrics using an electrically pulsed, non-equilibrium, inductively coupled glow discharge.  Following surface treatment the fabric samples were boil washed in water containing a readily available detergent between one and five times.  Fabric samples were either allowed to dry in the air or ironed. The results of the plasma treatment were compared with a traditional wet chemical fluorocarbon treatment.

The surface chemistry of the treated samples was investigated using high resolution XPS.

Survey spectrum of plasma treated nylon confirming a large amount of surface F incorporation.  Quantification of the XPS spectra gave 55% Fluorine on the surface.

Figure 1: Survey spectrum from plasma treated Nylon

The high resolution C 1s spectrum recorded at 10 eV pass energy, shown in Figure 2, demonstrates the excellent spectral resolution achieved on these irregular, highly insulating samples.  The resolution allows confident identification of many of the chemical functionalities present:
C-H; C-CF/C-CO₂; C-CF_n/C-O; C-F/C=O; CF-CF_n/CO₂; CF_2; and CF₃.

Figure 2: High resolution C 1s spectrum

Comparison of the surface fluorine content and the relative CF₂ concentration as found by XPS proves that the plasma deposition processes is more effective at coating the various fabrics used in the study.

Figure 3: Fluoride solvent (left) and plasma (right) fluorine concentration as a function of fabric

Results shown in the figure above show that after 5 washes the fluorosolvent wet chemical treated fabrics lost much of their fluorine functionalities.  The plasma treated fabrics performed generally better, retaining more of the surface ncoating and regaining much of the hidden fluorine functionalities after ironing.

Figure 4: comparison of fluorosolvent (left) and plasma (right) treated fabrics as a function of wash cycles

Overlay of C 1s spectra recorded from the wet chemical fluorosolvent treated fabric before washing, after 5 washes and after 5 washes and ironing.

Figure 5: High resolution C 1s of fluoro solvent treated fabric before washing (black), after 5 washes (red) and after 5 washes + ironing (blue)

High resolution C 1s spectrum of wet chemical fluorosolvent treated nylon after 1 wash and 5 washes demonstrating loss of surface coating.